There are many occasions and circumstances where it is desirable to monitor items within or passing through a specific area. More particularly, in the instances of vehicle or traffic monitoring it may be beneficial to be able to determine when or if a vehicle passes over a specific point such as might be determined by a vehicle passing over, near or in front of some type of sensor. Non-limiting examples of such vehicle detection include, traffic counting in travel lanes of a roadway, access gate control systems, and warning signal systems designed to warn or advise others of the approach or presence of a vehicle.
Previously available vehicle sensors have taken many forms including pneumatic hoses, optical sensors, radio frequency (RF) coils, electrical cables, and magnetic sensors, as well as other types of sensors. Common examples of such include pneumatic hoses stretched over roadways configured to operating air pressure sensitive switches as sensors for traffic counting stations. Similar configurations have been used as vehicle presence announcement devices in service stations and similar facilities.
Radio frequency (RF) coils have been embedded in roadways to detect passing traffic and at intersections to control traffic lights. More recently coaxial piezoelectric cables such as those disclosed in U.S. Pat. No. 5,477,217 to Bergan entitled “BIDIRECTIONAL ROAD TRAFFIC SENSOR” and U.S. Pat. No. 5,668,540 to Bailleul et al, entitled “DETECTION DEVICE FOR DATA RELATING TO THE PASSAGE OF VEHICLES ON A ROAD” have been suggested for use as a traffic sensor.
An important aspect to the operation of vehicle sensors is the long term reliability of such devices. Depending on operating environment, vehicle sensors may be subject to adverse conditions not only from environmental considerations, but also those resulting from interaction of the vehicles sought to be detected.
Additionally, although certain types of sensors may, after installation, be more protected from environmental conditions and vehicle interaction, they may require more complex construction and installation than might be warranted for some situations. For example, RF sensor coils may be embedded in a roadway by cutting grooves in the roadway and inserting wires into the grooves. Such installation may provide effective protection for the sensor but at a significant installation cost. Moreover, once installed, such RF coils are not readily relocatable if the vehicle detection requirements are only temporary.
Pneumatic hose type sensors may be easily installed by simply stretching them across a roadway and may just as easily be relocated if desired, but such sensors are subject to damage from the tires of the vehicles passing over the hose. In certain environments, for example where heavy trucks may be involved or the tires of such trucks may trap sensor damaging debris such as rocks within the treads, sensors may be easily and quickly damaged.
While various implementations of detection devices and systems have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.